Chemical mechanical polishing with napped poromeric

ABSTRACT

A method of polishing a substrate includes polishing a substrate with a generally linear polishing sheet, polishing the substrate with polishing pad composed of a napped poromeric material, and conditioning the polishing pad.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of pending U.S. patentapplication Ser. No. 11/531,272, filed Sep. 12, 2006, which is acontinuation of U.S. patent application Ser. No. 10/838,689, filed May3, 2004, now U.S. Pat. No. 7,104,875, which is a continuation of U.S.patent application Ser. No. 10/174,476, filed Jun. 17, 2002, now U.S.Pat. No. 6,729,944, which is a continuation of U.S. application Ser. No.09/302,570, filed Apr. 30, 1999, now U.S. Pat. No. 6,475,070, which is acontinuation-in-part of U.S. patent application Ser. No. 09/244,456,filed Feb. 4, 1999, now U.S. Pat. No. 6,244,935. The present applicationclaims priority to each of the above referenced patent applications, theentire contents of which patent applications are hereby incorporated byreference in their entirety.

BACKGROUND

The present invention relates to apparatus and methods for chemicalmechanical polishing a substrate, and more particularly to suchapparatus and methods using a moving polishing sheet.

An integrated circuit is typically formed on a substrate by thesequential deposition of conductive, semiconductive or insulative layerson a silicon wafer. One fabrication step involves depositing a fillerlayer over a patterned stop layer, and planarizing the filler layeruntil the stop layer is exposed. For example, trenches or holes in aninsulative layer may be filled with a conductive layer. Afterplanarization, the portions of the conductive layer remaining betweenthe raised pattern of the insulative layer form vias, plugs and linesthat provide conductive paths between thin film circuits on thesubstrate.

Chemical mechanical polishing (CMP) is one accepted method ofplanarization. This planarization method typically requires that thesubstrate be mounted on a carrier or polishing head. The exposed surfaceof the substrate is placed against a rotating polishing pad. Thepolishing pad may be either a “standard” pad or a fixed-abrasive pad. Astandard pad has a durable roughened surface, whereas a fixed-abrasivepad has abrasive particles held in a containment media. The carrier headprovides a controllable load, i.e., pressure, on the substrate to pushit against the polishing pad. A polishing slurry, including at least onechemically-reactive agent, and abrasive particles if a standard pad isused, is supplied to the surface of the polishing pad.

An effective CMP process not only provides a high polishing rate, butalso provides a substrate surface which is finished (lacks small-scaleroughness) and flat (lacks large-scale topography). The polishing rate,finish and flatness are determined by the pad and slurry combination,the relative speed between the substrate and pad, and the force pressingthe substrate against the pad. The polishing rate sets the time neededto polish a layer, which in turn sets the maximum throughput of the CMPapparatus.

During CMP operations, the polishing pad needs to be replacedperiodically. For a fixed-abrasive pad, the substrate wears away thecontainment media to expose the embedded abrasive particles. Thus, thefixed-abrasive pad is gradually consumed by the polishing process. Aftera sufficient number of polishing runs the fixed-abrasive pad needs to bereplaced. For a standard pad, the substrate thermally and mechanicallydamages the polishing pad and causes the pad's surface to becomesmoother and less abrasive. Therefore, standard pads must beperiodically “conditioned” to restore a roughened texture to theirsurface. After a sufficient number of conditioning operations (e.g.,three hundred to four hundred), the conditioning process consumes thepad or the pad is unable to be properly conditioned. The pad must thenbe replaced.

One problem encountered in the CMP process is difficulty in replacingthe polishing pad. The polishing pad may be attached to the platensurface with an adhesive. Significant physical effort is often requiredto peel the polishing pad away from the platen surface. The adhesivethen must be removed from the platen surface by scraping and washingwith a solvent. A new polishing pad can then be adhesively attached tothe clean surface of the platen. While this is happening, the platen isnot available for the polishing of substrates, resulting in a decreasein polishing throughput.

SUMMARY

In one aspect, the invention is directed to a chemical mechanicalpolishing apparatus that has a platen, a polishing sheet extendingbetween the a first reel and a second reel, and a motor to drive atleast one of the first and second reels to move the polishing sheet in alinear direction across the top surface of the platen during polishing.The polishing sheet has a width greater than a diameter of a substrateto be polished and has a portion extending over a top surface of theplaten for polishing the substrate.

Implementations of the invention may include the following. The motormay drive the first and second reels in a first direction to transferthe polishing sheet from the first reel to the second reel, and in asecond direction to transfer the polishing sheet from the second reel tothe first reel. A controller may cause the motor to alternate betweendriving the first and second reels in the first and second directions.The controller may be configured to cause the motor to decelerate whenone of the first and second reels is nearly empty. Also, the controllermay be configured to cause the motor to accelerate until the polishingsheet is moving at a desired speed, e.g., about one meter per second.The platen may include a plurality of passages to provide fluid to a topsurface of the platen and create a fluid bearing between the polishingsheet and the platen. A fluid source may be fluidly coupled to theplurality of passages. An actuator may move the platen, which may begenerally rectangular in shape, toward and away from the polishingsheet. A rotatable carrier head may hold the substrate. A frame and aplurality of retainers may secure the first and second reels to theframe. The polishing sheet may be a generally linear strip of a fixedabrasive polishing material.

In another aspect, the invention is directed to a chemical mechanicalpolishing apparatus that has a platen, a first roller, a second roller,a generally linear polishing sheet extending between the first andsecond rollers, and a motor to drive at least one of the first andsecond rollers to transfer the polishing sheet between the first andsecond rollers and move the polishing sheet in a linear direction acrossthe top surface of the platen. The polishing sheet has a width greaterthan a diameter of a substrate to be polished. The polishing sheet has afirst portion wound around the first roller, a second portion woundaround the second roller, and a third portion extending over a topsurface of the platen to polish the substrate.

In another aspect, the invention is directed to a chemical mechanicalpolishing apparatus that has a platen, a first roller, a second roller,a polishing sheet extending between the first and second rollers, amotor to drive the first and second rollers to move the polishing sheetacross the top surface of the platen, and a controller to cause themotor to alternately drive the polishing sheet in a first direction anda second, opposing direction during polishing of the substrate. Thepolishing sheet has a width greater than a diameter of a substrate to bepolished and has a portion extending over a top surface of the platenfor polishing the substrate.

In another aspect, the invention is directed to a method of chemicalmechanical polishing in which a substrate is brought into contact with apolishing sheet that extends between a first reel and a second reel, andthe first and second reels are driven to move the polishing sheet in alinear direction across a top surface of a platen during polishing. Thepolishing sheet has a width greater than a diameter of a substrate to bepolished.

Implementations of the invention may include the following. The firstand second reels may alternate between being driven in a first directionto transfer the polishing sheet from the first reel to the second reel,and in a second direction to transfer the polishing sheet from thesecond reel to the first reel. The first and second reels may deceleratewhen one of the first and second reels is nearly empty. The first andsecond reels may accelerate until the polishing sheet is moving at adesired speed, e.g., about one meter per second. A fluid may be injectedbetween a top surface of the platen and the polishing sheet to create afluid bearing therebetween. The platen may be moved vertically to adjusta pressure of the polishing sheet on the substrate. The substrate may berotated. The polishing sheet may be a fixed abrasive polishing material.A fluid may be injected between a surface of the substrate and thepolishing sheet through holes in the polishing sheet.

Advantages of the invention may include the following. More substratescan be polished without replacing the polishing pad, thereby reducingdowntime of the CMP apparatus and increasing throughput. A sheet offixed-abrasive polishing material can be provided in a polishingcartridge. It is easy to remove and replace the polishing cartridge froma platen. The polishing apparatus gains the advantages associated withfixed-abrasive polishing materials. A rotating carrier head can be usedto press the substrate against the polishing sheet. Lateral frictionalforces on the substrate can be reduced, thereby decreasing the load ofthe substrate against the retaining ring and improving polishinguniformity. The rigidity of the polishing sheet against the substratecan be adjusted independent of the polishing sheet material.

Other features and advantages will be apparent from the followingdescription, including the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic exploded perspective view of a chemical mechanicalpolishing apparatus.

FIG. 2 is a top view of the CMP apparatus of FIG. 1.

FIG. 3A is a top view of the first polishing station of the CMPapparatus of FIG. 1.

FIG. 3B is a schematic exploded perspective view of a rectangular platenand a polishing cartridge.

FIG. 3C is a schematic perspective view of a polishing cartridgeattached to a rectangular platen.

FIG. 4 is a schematic cross-sectional view of a fixed abrasive polishingsheet.

FIG. 5A is a schematic cross-sectional view of a feed roller of thepolishing cartridge of FIG. 3B.

FIG. 5B is a schematic exploded perspective view of the connection ofthe feed roller to the rectangular platen.

FIG. 6 is a schematic cross-sectional view of the polishing station ofFIG. 3A.

FIG. 7 is a schematic diagrammatic view of a polishing sheet advancingsystem.

FIG. 8 is a schematic partially cross-sectional and partiallyperspective view of a contamination guard system for a platen with anadvanceable polishing sheet.

FIG. 9 is a schematic cross-sectional view of a polishing station havingan optical endpoint detection system.

FIG. 10 is a schematic cross-sectional view of a platen and polishingpad of a second polishing station.

FIG. 11 is a schematic cross-sectional view of a platen and polishingpad of a final polishing station.

FIG. 12 is a schematic top view of a polishing station including apolishing sheet that moves in a linear direction across the substrateduring polishing.

FIG. 13 is a schematic cross-sectional side view of the polishingstation of FIG. 12.

FIGS. 14A and 14B are schematic cross-sectional views illustrating themotion of the polishing sheet during polishing.

FIG. 15 is a schematic top view of a polishing station that includes twopolishing cartridges and a rotatable platen.

FIG. 16 is a schematic exploded perspective view of the platen andpolishing cartridges of the polishing station of FIG. 15.

FIG. 17A is a schematic top view of a polishing station that includestwo polishing cartridges and a non-rotating platen, in which thepolishing sheets are driven in opposite directions.

FIG. 17B is a schematic top view of a polishing station that includestwo polishing cartridges and a non-rotating platen, in which thepolishing sheets are driven in the same direction.

FIG. 18 is a schematic cross-sectional view of the polishing station ofFIG. 17A.

FIG. 19A is a schematic top view of a polishing station that includesthree polishing cartridges and a rotating platen.

FIG. 19B is a schematic top view of a polishing station that includesthree polishing cartridges and a non-rotating platen.

Like reference numbers are used in the various drawings to indicate likeelements. A primed reference number indicates an element that has amodified function, operation or structure.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, one or more substrates 10 will be polishedby a chemical mechanical polishing apparatus 20. A description of asimilar polishing apparatus may be found in U.S. Pat. No. 5,738,574, theentire disclosure of which is incorporated herein by reference.Polishing apparatus 20 includes a machine base 22 with a table top 23that supports a series of polishing stations, including a firstpolishing station 25 a, a second polishing station 25 b, and a finalpolishing station 25 c, and a transfer station 27. Transfer station 27serves multiple functions, including receiving individual substrates 10from a loading apparatus (not shown), washing the substrates, loadingthe substrates into carrier heads, receiving the substrates from thecarrier heads, washing the substrates again, and finally, transferringthe substrates back to the loading apparatus.

Each polishing station includes a rotatable platen. At least one of thepolishing stations, such as first station 25 a, includes a polishingcartridge 102 mounted to a rotatable, rectangular platen 100. Thepolishing cartridge 102 includes a linearly advanceable sheet or belt offixed-abrasive polishing material. The remaining polishing stations,e.g., second polishing station 25 b and final polishing station 25 c,may include “standard” polishing pads 32 and 34, respectively, eachadhesively attached to a circular platen 30. Each platen may beconnected to a platen drive motor (not shown) that rotates the platen atthirty to two hundred revolutions per minute, although lower or higherrotational speeds may be used. Assuming that substrate 10 is an“eight-inch” (200 mm) diameter disk, then rectangular platen 100 may beabout twenty inches on a side, and circular platen 30 and polishing pads32 and 34 may be about thirty inches in diameter.

Each polishing station 25 a, 25 b and 25 c also includes a combinedslurry/rinse arm 52 that projects over the associated polishing surface.Each slurry/rinse arm 52 may include two or more slurry supply tubes toprovide a polishing liquid, slurry, or cleaning liquid to the surface ofthe polishing pad. For example, the polishing liquid dispensed onto thefixed-abrasive polishing sheet at first polishing station 25 a will notinclude abrasive particles, whereas the slurry dispensed onto thestandard polishing pad at second polishing station 25 b will includeabrasive particles. If final polishing station 25 a is used for buffing,the polishing liquid dispensed onto the polishing pad at that stationwould not include abrasive particles. Typically, sufficient liquid isprovided to cover and wet the entire polishing pad. Each slurry/rinsearm also includes several spray nozzles (not shown) which provide ahigh-pressure rinse at the end of each polishing and conditioning cycle.

The polishing stations that include a standard polishing pad, i.e.,polishing station 25 b and 25 c, may include an optional associated padconditioner apparatus 40. The pad conditioner apparatus can include aconditioner head suspended on the distal end of an arm. The proximal endof the arm is supported by a support assembly which can rotate theentire arm so as to place the conditioning head in place for padconditioning and to sweep it over the pad. The conditioner head holds atoothed or otherwise very abrasive surface conditioning disk or othergenerally cylindrical member. The conditioning disk is held by aflexible holding pad having a lower magnetic face. The conditioning diskis made of a magnetic material that is held to the magnetic side of theholding pad, and its other side is impregnated with diamonds forscraping the polishing pad.

The polishing stations that include a fixed-abrasive polishing pad,i.e., polishing station 25 a, may include an optional unillustratedcleaning apparatus to remove grit or polishing debris from the surfaceof the polishing sheet. The cleaning apparatus may include a rotatablebrush to sweep the surface of the polishing sheet and/or a nozzle tospray a pressurized cleaning liquid, e.g., deionized water, onto thesurface of the polishing sheet. The cleaning apparatus can be operatedcontinuously, or between polishing operations. In addition, the cleaningapparatus could be stationary, or it could sweep across the surface ofthe polishing sheet.

In addition, optional cleaning stations 45 may be positioned betweenpolishing stations 25 a and 25 b, between polishing stations 25 b and 25c, between polishing station 25 c and transfer station 27, and betweentransfer station 27 and polishing station 25 a, to clean the substrateas it moves between the stations.

A rotatable multi-head carousel 60 is supported above the polishingstations by a center post 62 and is rotated about a carousel axis 64 bya carousel motor assembly (not shown). Carousel 60 includes four carrierhead systems mounted on a carousel support plate 66 at equal angularintervals about carousel axis 64. Three of the carrier head systemsreceive and hold substrates, and polish them by pressing them againstthe polishing sheet of station 25 a and the polishing pads of stations25 b and 25 c. One of the carrier head systems receives a substrate fromand delivers a substrate to transfer station 27.

Each carrier head system includes a carrier or carrier head 80. Acarrier drive shaft 78 connects a carrier head rotation motor 76 (shownby the removal of one quarter of the carousel cover) to carrier head 80so that each carrier head can independently rotate about its own axis.In addition, each carrier head 80 independently laterally oscillates ina radial slot 72 formed in carousel support plate 66.

The carrier head 80 performs several mechanical functions. Generally,the carrier head holds the substrate against the polishing surface,evenly distributes a downward pressure across the back surface of thesubstrate, transfers torque from the drive shaft to the substrate, andensures that the substrate does not slip out from beneath the carrierhead during polishing operations. A description of a suitable carrierhead may be found in U.S. patent application Ser. No. 08/861,260,entitled a CARRIER HEAD WITH a FLEXIBLE MEMBRANE FOR a CHEMICALMECHANICAL POLISHING SYSTEM, filed May 21, 1997 by Steven M. Zuniga etal., assigned to the assignee of the present invention, the entiredisclosure of which is incorporated herein by reference.

Referring to FIGS. 3A, 3B, and 3C, polishing cartridge 102 is detachablysecured to rectangular platen 100 at polishing station 25 a. Polishingcartridge 102 includes a feed roller 130, a take-up roller 132, and agenerally linear sheet or belt 110 of a polishing pad material. Anunused or “fresh” portion 120 of the polishing sheet is wrapped aroundfeed roller 130, and a used portion 122 of the polishing sheet iswrapped around take-up roller 132. A rectangular exposed portion 124 ofthe polishing sheet that is used to polish substrates extends betweenthe used and unused portions 120, 122 over a top surface 140 ofrectangular platen 100.

The rectangular platen 100 can be rotated (as shown by phantom arrow “A”in FIG. 3A) to rotate the exposed portion of the polishing sheet andthereby provide relative motion between the substrate and the polishingsheet during polishing. Between polishing operations, the polishingsheet can be advanced (as shown by phantom arrow “B” in FIG. 3A) toexpose an unused portion of the polishing sheet. When the polishingmaterial advances, polishing sheet 110 unwraps from feed roller 130,moves across the top surface of the rectangular platen, and is taken upby take-up roller 132.

Referring to FIG. 4, polishing sheet 110 is preferably a fixed-abrasivepolishing pad having a polishing surface 112. The fixed-abrasivepolishing pad may be about twenty inches wide and about 0.005 inchesthick. The fixed-abrasive polishing pad may include an upper layer 114and a lower layer 116. Upper layer 114 is an abrasive composite layercomposed of abrasive grains held or embedded in a binder material. Theabrasive grains may have a particle size between about 0.1 and 1500microns. Examples of such grains include silicon oxide, fused aluminumoxide, ceramic aluminum oxide, green silicon carbide, silicon carbide,chromia, alumina zirconia, diamond, iron oxide, ceria, cubic boronnitride, garnet and combinations thereof. The binder material may bederived from a precursor which includes an organic polymerizable resinwhich is cured to form the binder material. Examples of such resinsinclude phenolic resins, urea-formaldehyde resins, melamine formaldehyderesins, acrylated urethanes, acrylated epoxies, ethylenicallyunsaturated compounds, aminoplast derivatives having at least onependant acrylate group, isocyanurate derivatives having at least onependant acrylate group, vinyl ethers, epoxy resins, and combinationsthereof. Lower layer 116 is a backing layer composed of a material suchas a polymeric film, paper, cloth, a metallic film or the like. Afixed-abrasive polishing sheet having a polyester belt that carriessilicon oxide abrasive particles is available from 3M Corporation ofMinneapolis, Minn.

Referring again to FIGS. 3A, 3B and 3C, a transparent strip 118 isformed along the length of polishing sheet 110. The transparent stripmay be positioned at the center of the sheet, and may be about 0.6inches wide. Transparent strip 118 may be formed by excluding abrasiveparticles from this region of the containment media during fabricationof the polishing sheet. The transparent strip will be aligned with anaperture or transparent window 154 in rectangular platen 100 to provideoptical monitoring of the substrate surface for end point detection, asdiscussed in greater detail below.

The feed and take-up rollers 130 and 132 should be slightly longer thanthe width of polishing sheet 110. The rollers 130, 132 may be plastic ormetal cylinders about 20″ long and about 2″ in diameter. Referring toFIG. 5A, the opposing end faces 134 of feed roller 130 (only the feedroller is shown, but the take-up roller would be constructed similarly)each include a recess 136 which will engage a support pin 164 (see FIGS.3B and 5B) that will secure the roller to the platen. In addition, bothend faces 134 of each roller may be chamfered at edge 138 to preventpolishing sheet 110 from slipping laterally.

Returning to FIGS. 3A, 3B and 3C, rectangular platen 100 includes agenerally planar rectangular top surface 140 bounded by a feed edge 142,a take-up edge 144, and two parallel lateral edges 146. A groove 150(shown in phantom in FIGS. 3A and 3C) is formed in top surface 140. Thegroove 150 may be a generally-rectangular pattern that extends alongedges 142-146 of top surface 140. A passage 152 through platen 100connects groove 150 to a vacuum source 200 (see FIG. 6). When passage152 is evacuated, exposed portion 124 of polishing sheet 110 isvacuum-chucked to top surface 140 of platen 100. This vacuum-chuckinghelps ensure that lateral forces caused by friction between thesubstrate and the polishing sheet during polishing do not force thepolishing sheet off the platen. A central region 148 of top surface 140is free from grooves to prevent potential deflection of the polishingsheet into the grooves from interfering with the polishing uniformity.As discussed, aperture 154 is formed in top surface 140 of rectangularplaten 100. An unillustrated compressible backing pad may be placed onthe top surface of the platen to cushion the impact of the substrateagainst the polishing sheet. In addition, platen 100 may include anunillustrated shim plate. Shim plates of differing thickness may beattached to the platen to adjust the vertical position of the topsurface of platen. The compressible backing pad can be attached to theshim plate.

The rectangular platen 100 also includes four retainers 160 that holdfeed and take-up rollers 130 and 132 at feed and take-up edges 142 and144, respectively. Each retainer 160 includes an aperture 162. At eachretainer, a pin 164 extends through aperture 162 and into recess 136(see FIG. 5A) to rotatably connect rollers 130 and 132 to platen 100. Tosecure polishing cartridge 102 to platen 100, feed roller 130 is slippedinto the space between the two retainers along feed edge 142, and twopins 164 are inserted through opposing apertures 162 in retainers 160 toengage the two opposing recesses in the feed roller. Similarly, take-uproller 132 is mounted to platen 100 by slipping it into place betweenthe two retainers along take-up edge 144, and inserting two pins 164through the opposing apertures 162 to engage the two opposing recessesin the take-up roller.

As shown in FIG. 5B, one pin 164 from each roller 130, 132 may passthrough a gear assembly 166 a, 166 b (see also FIG. 7) that controls therotation of the pin, and thus the rotation of the roller. Gear assembly166 a may be secured to the side of rectangular platen 100 by screws orbolts 167, and a cover 168 may protect gear assembly 166 fromcontamination during the polishing process.

The rollers 130 and 132 need to be positioned sufficiently below topsurface 140 so that the polishing sheet stays in contact with the feedand take-up edges 142 and 144 of the platen when the entire polishingsheet is wound around either roller. This assists in the creation of aseal between the polishing sheet and the rectangular platen when vacuumis applied to passage 152 to vacuum-chuck the polishing sheet to theplaten. Furthermore, feed edge 142 and take-up edge 144 of the platenare rounded to prevent abrasion of the underside of the polishing sheetas it moves across the platen.

As illustrated by FIG. 6, rectangular platen 100 is secured to arotatable platen base 170. Rectangular platen 100 and platen base 170may be joined by several peripheral screws 174 counter-sunk into thebottom of platen base 170. A first collar 176 is connected by screws 178to the bottom of platen base 170 to capture the inner race of an annularbearing 180. A second collar 182, connected to table top 23 by a set ofscrews 183, captures the outer race of annular bearing 180. Annularbearing 180 supports rectangular platen 100 above table top 23 whilepermitting the platen to be rotated by the platen drive motor.

A platen motor assembly 184 is bolted to the bottom of table top 23through a mounting bracket 186. Platen motor assembly 184 includes amotor 188 having an output drive shaft 190. Output shaft 190 is fittedto a solid motor sheath 192. A drive belt 194 winds around motor sheath192 and a hub sheath 196. Hub sheath 196 is joined to platen base 170 bya platen hub 198. Thus, motor 188 may rotate rectangular platen 100.Platen hub 198 is sealed to lower platen base 170 and to hub sheath 196.

A pneumatic control line 172 extends through rectangular platen 100 toconnect passage 152, and thus grooves 150, to a vacuum or pressuresource. The pneumatic line 172 may be used both to vacuum-chuck thepolishing sheet, and to power or activate a polishing sheet advancementmechanism, described in greater detail below.

The platen vacuum-chucking mechanism and the polishing sheet advancingmechanism may be powered by a stationary pneumatic source 200 such as apump or a source of pressurized gas. Pneumatic source 200 is connectedby a fluid line 202 to a computer controlled valve 204. The computercontrolled valve 204 is connected by a second fluid line 206 to a rotarycoupling 208. The rotary coupling 208 connects the pneumatic source 200to an axial passage 210 in a rotating shaft 212, and a coupling 214connects axial passage 210 to a flexible pneumatic line 216.

Vacuum-chucking passage 152 can be connected to flexible pneumatic line216 via pneumatic line 172 through rectangular platen 100, a passage 220in platen base 170, a vertical passage 222 in platen hub 198, and apassageway 224 in hub sheath 196. O-rings 226 may be used to seal eachpassageway.

A general purpose programmable digital computer 280 is appropriatelyconnected to valve 204, platen drive motor 188, carrier head rotationmotor 76, and a carrier head radial drive motor (not shown). Computer280 can open or close valve 204, rotate platen 100, rotate carrier head80 and move carrier head along slot 72.

Referring to FIGS. 5B and 7, the polishing cartridge and platen includesa sheet advancing mechanism to incrementally advance polishing sheet110. Specifically, gear assembly 166 a adjacent feed roller 130 includesa feed gear wheel 230 that is rotationally fixed to pin 164. The feedgear wheel 230 engages a ratchet 232 that is held in place by anescapement clutch 234. Ratchet 232 and escapement clutch 234 may becontained in gear assembly 166 a, and thus are not shown in FIG. 5B.

The gear assembly 166 b (not shown in FIG. 5B) adjacent take-up roller132 includes a take-up gear wheel 240 that is rotationally fixed to pin164. The take-up gear wheel 240 engages a slip clutch 244 and a torsionspring 242. The torsion spring 242 applies a constant torque that tendsto rotate the take-up roller and advance the polishing sheet. Inaddition, slip clutch 244 prevents take-up roller 132 from rotatingcounter to the torque applied by torsion spring 242.

While ratchet 232 engages feed gear wheel 230 on feed roller 130,polishing sheet 110 cannot advance. Thus, torsion spring 242 and slipclutch 244 maintain polishing sheet 110 in a state of tension with theexposed portion of the polishing sheet stretched across the top surfaceof rectangular platen 100. However, if escapement clutch 234 isactivated, ratchet 232 disengages from feed gear wheel 230, and take-uproller 132 can rotate until feed gear wheel 230 reengages ratchet 232,e.g., by one notch. Escapement clutch 234 can be pneumaticallycontrolled by the same pneumatic line 172 that is used to vacuum chuckthe polishing sheet 110 to platen 100. An unillustrated tube may connectpneumatic line 172 to gear assembly 166 a. If a positive pressure isapplied to pneumatic line 172, escapement clutch 234 is activated tomove ratchet 232. This permits the feed roller to rotate one notch, witha corresponding advancement of the polishing sheet across the platen. Aseparate pneumatic line could control escapement clutch 234, althoughthis would require an additional rotary feed-through. Alternately, thelinear drive mechanism may include a ratchet 169 (see FIG. 5B) thatengages one of the gear assemblies to manually advance the polishingsheet.

A potential problem during polishing is that the unused portion of thepolishing sheet may become contaminated by slurry or polishing debris.Referring to FIG. 8, a portion 156 of rectangular platen 100 may projectover feed roller 130 so that the feed roller is located beneath theplaten top surface and inwardly of the feed edge of the platen. As such,the body of the platen shields the feed roll from contamination.Alternately, an elongated cover with a generally semicircularcross-section can be positioned around each roller. The elongated covercan be secured to the retainers. The polishing sheet would pass througha thin gap between the cover and the platen.

In addition, a contamination guard 250 can be positioned over the feededge of the rectangular platen. The contamination guard includes a frame252 that extends along the width of polishing sheet 110 and is suspendedabove the sheet to form a narrow gap 254. A fluid source (not shown),such as a pump, forces a gas, such as air, through gap 254 viapassageway 256 to provide a uniform air flow as shown by arrows 258. Theflow of air through gap 254 prevents the polishing liquid or polishingdebris from passing beneath contamination guard 250 and contaminatingthe unused portion of the polishing sheet on feed roller 130.

Referring to FIG. 9, an aperture or hole 154 is formed in platen 100 andis aligned with transparent strip 118 in polishing sheet 110. Theaperture 154 and transparent strip 118 are positioned such that theyhave a “view” of substrate 10 during a portion of the platen's rotation,regardless of the transnational position of the polishing head. Anoptical monitoring system 90 is located below and secured to platen 100,e.g., between rectangular platen 100 and platen base 170 so that itrotates with the platen. The optical monitoring system includes a lightsource 94, such as a laser, and a detector 96. The light sourcegenerates a light beam 92 which propagates through aperture 154 andtransparent strip 118 to impinge upon the exposed surface of substrate10.

In operation, CMP apparatus 20 uses optical monitoring system 90 todetermine the thickness of a layer on the substrate, to determine theamount of material removed from the surface of the substrate, or todetermine when the surface has become planarized. The computer 280 maybe connected to light source 94 and detector 96. Electrical couplingsbetween the computer and the optical monitoring system may be formedthrough rotary coupling 208. The computer may be programmed to activatethe light source when the substrate overlies the window, to storemeasurements from the detector, to display the measurements on an outputdevice 98, and to detect the polishing endpoint, as described in U.S.patent application Ser. No. 08/689,930, entitled METHOD OF FORMING ATRANSPARENT WINDOW IN A POLISHING PAD FOR A CHEMICAL MECHANICALPOLISHING APPARATUS, filed Aug. 16, 1996 by Manush Birang et al.,assigned to the assignee of the present invention, the entire disclosureof which is incorporated herein by reference.

In operation, exposed portion 124 of polishing sheet 110 isvacuum-chucked to rectangular platen 100 by applying a vacuum to passage152. A substrate is lowered into contact with polishing sheet 110 bycarrier head 80, and both platen 100 and carrier head 80 rotate topolish the exposed surface of the substrate. After polishing, thesubstrate is lifted off the polishing pad by the carrier head. Thevacuum on passage 152 is removed. The polishing sheet is advanced byapplying a positive pressure to pneumatic line 172 to trigger theadvancement mechanism. This exposes a fresh segment of the polishingsheet. The polishing sheet is then vacuum-chucked to the rectangularplaten, and a new substrate is lowered into contact with the polishingsheet. Thus, between each polishing operation, the polishing sheet maybe advanced incrementally. If the polishing station includes a cleaningapparatus, the polishing sheet may be washed between each polishingoperation.

The amount that the sheet may be advanced will depend on the desiredpolishing uniformity and the properties of the polishing sheet, butshould be on the order of 0.05 to 1.0 inches, e.g., 0.4 inch, perpolishing operation. Assuming that the exposed portion 124 of polishingsheet is 20 inches long and the polishing sheet advances 0.4 inchesafter each polishing operation, the entire exposed portion of thepolishing sheet will be replaced after about fifty polishing operations.

Referring to FIG. 10, at second polishing station 25 b, the circularplaten may support a circular polishing pad 32 having a roughed surface262, an upper layer 264 and a lower layer 266. Lower layer 266 may beattached to platen 30 by a pressure-sensitive adhesive layer 268. Upperlayer 264 may be harder than lower layer 266. For example, upper layer264 may be composed of microporous polyurethane or polyurethane mixedwith a filler, whereas lower layer 266 may be composed of compressedfelt fibers leached with urethane. A two-layer polishing pad, with theupper layer composed of IC-1000 or IC-1400 and the lower layer composedof SUBA-4, is available from Rodel, Inc. of Newark, Del. (IC-1000,IC-1400 and SUBA-4 are product names of Rodel, Inc.). A transparentwindow 269 may be formed in polishing pad 32 over an aperture 36 inplaten 30.

Referring to FIG. 11, at final polishing station 25 c, the platen maysupport a polishing pad 34 having a generally smooth surface 272 and asingle soft layer 274. Layer 274 may be attached to platen 30 by apressure-sensitive adhesive layer 278. Layer 274 may be composed of anapped poromeric synthetic material. A suitable soft polishing pad isavailable from Rodel, Inc., under the trade name Polytex. Polishing pads32 and 34 may be embossed or stamped with a pattern to improvedistribution of slurry across the face of the substrate. Polishingstation 25 c may otherwise be identical to polishing station 25 b. Atransparent window 279 may be formed in polishing pad 34 over aperture36.

Although the CMP apparatus is described a vacuum chucking the polishingsheet to the platen, other techniques could be used to secure thepolishing sheet to the platen during polishing. For example, the edgesof the polishing sheet could be clamped to the sides of the platen by aset of clamps.

Also, although the rollers are described as connected to the retainersby pins that are inserted through apertures, numerous otherimplantations are possible to rotatably connect the rollers to theplaten. For example, a recess could be formed on the inner surface ofthe retainer to engage a pin that projects from the end face of theroller. The retainers 160 may be slightly bendable, and the rollersmight be snap-fit into the retainers. Alternately, the recess in theinner surface of the retainer could form a labyrinth path that traps therollers due to tension. Alternately, the retainer could be pivotallyattached to the platen, and the roller could engage the retainer oncethe retainer is locked in position.

In addition, although the CMP apparatus is described as having onerectangular platen with a fixed-abrasive polishing sheet and twocircular platens with standard polishing pads, other configurations arepossible. For example, the apparatus can include one, two or threerectangular platens. In fact, one advantage of CMP apparatus 20 is thateach platen base 170 is adaptable to receive either a rectangular platenor a circular platen. The polishing sheet on each rectangular platen maybe a fixed abrasive or a non-fixed abrasive polishing material.Similarly, each polishing pad on the circular platen can be afixed-abrasive or a non-fixed abrasive polishing material. The standardpolishing pads can have a single hard layer (e.g., IC-1000), a singlesoft layer (e.g., as in a Polytex pad), or two stacked layers (e.g., asin a combined IC-1000/SUBA IV polishing pad). Different slurries anddifferent polishing parameters, e.g., carrier head rotation rate, platenrotation rate, carrier head pressure, can be used at the differentpolishing stations.

One implementation of the CMP apparatus may include two rectangularplatens with fixed-abrasive polishing sheets for primary polishing, anda circular platen with a soft polishing pad for buffing. The polishingparameters, pad composition and slurry composition can be selected sothat the first polishing sheet has a faster polishing rate than thesecond polishing sheet.

Referring to FIGS. 12 and 13, in another implementation, at least one ofthe polishing stations, e.g., the first polishing station, includes apolishing cartridge 102′ and a non-rotating platen 300. Polishingcartridge 102′ includes a first roller or reel 130′, a second roller orreel 132′, and a generally linear sheet or belt 110′ of polishingmaterial, such as a fixed-abrasive polishing material. A first portion120′ of the polishing sheet is wrapped around the first roller 130′, anda second portion 122′ of the polishing sheet is wrapped around secondroller 132′. An exposed portion 124′ of the polishing sheet extends overthe platen between the first and second rollers.

Four retainers 310 (shown in phantom in FIG. 13) are secured to tabletop 23 at the polishing station. Polishing cartridge 102′ is detachablysecured by retainers 310 to the table top. As discussed above, differentimplementations are possible to connect the polishing cartridge to theretainers. For example, the opposing end faces of rollers 130′, 132′ mayengage support pins 312 that will rotatably connect the rollers to theassociated retainers.

A drive mechanism 320 controls the rotation of the rollers 130′ and132′. The drive mechanism 320 can include two motors 322. One motorrotates first roller 130′, and the other motor rotates second roller132′. Each roller can be driven by its associated motor 322 in itsrespective take-up direction. It should be noted that as the polishingsheet is wound on the take-up roller, the effective diameter of theroller changes, thereby changing the take-up speed of that roller(assuming the roller rotates at a constant angular velocity). By drivingone roller at a time in its respective take-up direction, the polishingsheet remains in tension, independent of the effective diameter of thetake-up roller. Of course, many other drive mechanisms are possible. Forexample, with a more complex drive mechanism, both rollers could bedriven by a single motor.

During polishing, polishing sheet 110′ is driven linearly across theexposed portion of the substrate by drive mechanism 320 to providerelative motion between the substrate and the polishing sheet. As shownin FIG. 14A, the polishing sheet is initially driven (as shown by arrow“C”) from first roller 130′ to second roller 132′. Specifically, thepolishing sheet unwinds from first roller 130′, moves across the topsurface of the platen, and is taken up by second roller 132′. As shownin FIG. 14B, once first roller 130′ is empty and second roller 132′ isfull, the polishing sheet reverses direction, and the polishing sheet isdriven (as shown by arrow “D”) from second roller 132′ to first roller130′. Specifically, the polishing sheet unwinds from second roller 132′,moves across the top surface of the rectangular platen, and is taken upby first roller 130′. Once first roller 130′ is full and second roller132′ is empty, the polishing sheet reverses direction again, and isdriven from first roller 130′ to second roller 132′. In sum, thepolishing sheet is driven alternately in one direction, and then in thereverse direction, until polishing of the substrate is complete.

The appropriate speed of the polishing sheet will depend on the desiredpolishing rate and the polishing sheet properties, but should be on theorder of about one meter/second. The driving motor 322 may deceleratewhen a roller is nearly empty to prevent the polishing sheet frombreaking under excessive stress. In addition, when the polishing sheetreverses direction, the motor will accelerate to bring the polishingsheet up to the desired polishing speed. Therefore, the speed of thepolishing sheet will not necessarily be uniform.

Returning to FIGS. 12 and 13, platen 300 includes a generally planarrectangular top surface 302. A plurality of passages 304 (shown inphantom in FIG. 12) are formed through platen 300. A fluid supply line306 connects passages 304 to a fluid source 308. During polishing, fluidis forced through passages 304 into a gap 309 between the top surface ofthe platen and the polishing sheet to form a fluid bearing therebetween.This fluid bearing helps ensure that the polishing sheet does not becomeabraded or stuck to the platen during polishing. In addition, ifapertures or holes are formed in the polishing sheet, one of thepassages can be used to inject a polishing fluid, e.g., a mixture ofchemicals to aid the polishing process, through the holes in thepolishing sheet and between the substrate surface and the polishingsheet.

The platen 300 may be vertically movable to adjust the pressure of thepolishing sheet against the substrate. An actuator 330, such as apneumatic actuator or a pressurizable bellows, may connect platen 300 tothe table top of the CMP apparatus to raise and lower the platen asnecessary.

Referring to FIGS. 15 and 16, in another implementation, at least onepolishing station, e.g., the first polishing station, includes a firstpolishing cartridge 350, a second polishing cartridge 360, and arotatable rectangular platen 370. The first polishing cartridge 350includes a first roller or reel 352, a second roller or reel 354, and agenerally linear sheet or belt 356 constructed of, for example, afixed-abrasive polishing material. Similarly, second polishing cartridge360 includes a first roller or reel 362, a second roller or reel 364,and a generally linear sheet or belt 366 constructed of, for example, afixed-abrasive polishing material. The polishing sheets 356, 366 may beconstructed of the same polishing material or different polishingmaterials.

The polishing cartridges 350, 360 can be mounted on platen 370 withretainers 371 so that the exposed portions of polishing sheets 356, 366are arranged in two parallel coplanar strips separated by a relativelynarrow gap 372. During polishing, platen 370 is rotated to createrelative motion between the substrate and the polishing sheets (the areaswept by substrate 10 during polishing is shown by phantom line 379).Between polishing operations, the polishing sheets are advancedincrementally to expose an unused portion of the polishing sheet. Thepolishing sheets 356, 366 can be advanced incrementally in the samedirection, or in opposite directions.

Two grooves 376 (shown in phantom in FIG. 15) are formed in a topsurface 378 of platen 370. Each groove forms a generally rectangularpattern, with one polishing sheet overlying each groove. Both groovesare connected to a vacuum source to vacuum chuck their respectivepolishing sheets to the platen.

An elongated transparent window 374 is formed in platen 370 and alignedwith the gap between polishing sheets 356 and 366. The opticalmonitoring system can direct a light beam through window 374 and gap 372to impinge the substrate being polished. An advantage of thisimplementation is that does not require a polishing sheet having atransparent stripe.

Referring to FIG. 17A, in another implementation, at least one polishingstation, e.g., the first polishing station, includes a first polishingcartridge 350′ and a second polishing cartridge 360′ mounted to themachine base over a non-rotating platen 370′. The first polishingcartridge 350′ includes a first roller or reel 352′, a second roller orreel 354′, and a generally linear sheet or belt 356′ of a fixed-abrasivepolishing material. Similarly, second polishing cartridge 360′ includesa first roller or reel 362′, a second roller or reel 364′, and agenerally linear sheet or belt 366′ of a fixed-abrasive polishingmaterial. The exposed portions of polishing sheets 356′, 366′ arearranged in two parallel coplanar strips separated by a relativelynarrow gap 372′. Substrate 10 (shown in phantom) is positioned tooverlie both polishing sheets 354′, 364′.

Referring to FIG. 18, platen 370′ includes a first fluid bearing surface380 underlying first polishing sheet 356′, a second fluid bearingsurface 382 underlying second polishing sheet 366′, and a channel 384(shown in phantom in FIG. 17) separating the bearing surfaces. Inaddition, channels 385 may be formed along the outer edges of thebearing surfaces. During polishing, the polishing liquids will flow offthe edges of the polishing sheets and into channels 384 and 385.Passages 388 extends through platen 380 to provide drainage of thepolishing liquid from channels 384 and 385 via an outlet 387. Atransparent window 386 positioned in channel 384 provides a viewing portfor optical monitoring system 90′. Specifically, optical monitoringsystem 90′ can direct a light beam 92′ through window 386 and gap 372′to impinge the surface of the substrate being polished. Window 386should project above the bottom of channel 384, but not above bearingsurfaces 380 and 382. Thus, the window provides a substantiallyunblocked view of the bottom surface of the substrate during polishing.In addition, passages 390 are formed through platen 370′. A fluid source391 is coupled to passages 390 to inject fluid between the bearingsurfaces and the lower surface of the polishing sheets.

Returning to FIG. 17A, during polishing, the polishing sheets 354′, 364′are driven alternately in one direction and then in the reversedirection. Specifically, a first pair of motors 392 and 394 can drivethe first pair of rollers 352′ and 362′, respectively, and a second pairof motors 396 and 398 can drive the second pair of rollers 354′ and364′. The polishing sheets 354′ and 364′ can be driven by motors 392,394 and 396, 398, in opposite directions (as shown by arrows E and F,respectively). The substrate can be rotated and/or oscillated laterallyat a relatively low speed in order to avoid a low removal rate in theregion of the substrate overlying the gap.

Alternately, referring to FIG. 17B, polishing sheets 354′, 364′ can bedriven in the same direction (as shown by arrows G and H, respectively).In this case, rollers 352″, 362″ can be rotationally coupled, e.g., by adrive shaft 358. Similarly, rollers 354″, 364″ can be rotationallycoupled, e.g., by a drive shaft 368. A first motor 392′ can driverollers 352″, 362″, and a second motor 396′ can drive rollers 354″,364″. Thus, both polishing sheets would move in the same direction andat the same speed. In addition, each pair of rollers could be replacedby a single roller that carries the two separate polishing sheets. Inthis case, the central retainer could be eliminated.

Referring to FIG. 19A, in yet another implementation, at least one ofthe polishing stations, e.g., the first polishing station, includes aninner polishing cartridge 400 and two outer polishing cartridges 410.The inner polishing cartridge 400 includes a first roller or reel 402, asecond roller or reel 404, and a generally linear sheet or belt 406 of afixed-abrasive polishing material. Similarly, each outer polishingcartridge 410 includes a first roller or reel 412, a second roller orreel 414, and a generally linear sheet or belt 416 of a fixed-abrasivepolishing material. The inner and outer polishing sheets 406, 416 arearranged in three substantially parallel strips, each strip separated bya relatively narrow gap 420. The optical monitoring system may direct alight beam onto the surface of substrate through one of the gaps betweenthe polishing sheets. The rollers 412, 414 of outer cartridge 410 arepositioned in a rectangular configuration. In addition, the rollers 402,404 of central cartridge 400 are spaced further apart than the rollersof the outer cartridges. Consequently, the exposed portion of centralpolishing sheet 406 is longer than the exposed portion of either outerpolishing sheet 416.

As shown in FIG. 19A, the polishing cartridges can be mounted to arotatable platen 430 (similar to the implementation shown in FIGS. 15and 16), and the polishing sheets can be moved incrementally betweenpolishing operations. The drive systems for the cartridges are notshown, but could be similar that illustrated in the implementation ofFIGS. 3A-7. As the platen rotates, substrate 10 sweeps over a path(shown by phantom line 432) that covers each of the polishing sheets.The staggered position of the rollers reduces the diagonal length of therotatable platen, thereby reducing the radius of the circle (shown byphantom line 434) swept by the platen and using space more efficiently.

Alternately, as shown in FIG. 19B, the polishing cartridges can bemounted to the machine base over a non-rotating platen 430′ (similar tothe implementation shown in FIGS. 17A and 18), and the polishing sheetscan be moved continuously during polishing. Central polishing sheet 406′can be driven by a pair of motors 408, whereas outer polishing sheets416′ can be driven two pairs of motors 418. Each polishing sheet can bedriven alternately in one direction by one of the motors, and then inthe opposite direction by the other motor. Of course, if outer polishingsheets 416′ are to be driven in the same direction, the outer rollers412′ and 414′ can have common drive shafts. In this case, the outerpolishing sheets can be driven by a single pair of motors. Substrate 10is positioned to overlie at least two, and preferably all three,polishing sheets. The substrate can be rotated and/or oscillatedlaterally at a relatively low speed in order to avoid a low removal ratein the region of the substrate overlying the gaps.

In the implementation of FIG. 19B, the central polishing sheet can bedriven in the opposite direction as the outer polishing sheets (as shownby arrows I and J, respectively). In fact, the three polishing sheetscan be driven to reduce or substantially eliminate (as compared to aconventional rotating or linear polishing system) the total lateralforce, i.e., the force in the plane of the substrate, on the substrate.Specifically, if the central and outer polishing sheets are driven atsubstantially the same speed but opposite directions, and if the surfacearea 424 of the substrate contacting the outer polishing sheets issubstantially equal to the surface area 422 of the substrate contactingthe central polishing sheet, the frictional forces applied to thesubstrate will substantially cancel each other. As a result, the totallateral force on the substrate is reduced or substantially eliminated,without creating a significant torque on the substrate. This shoulddecrease the load of the substrate against the retaining ring, therebyreducing substrate deformation and improving polishing uniformity. Ifsurface area 422 is greater or less than surface area 424, the relativespeeds of the polishing sheets can be adjusted so that the total lateralforce is substantially reduced.

In addition, the polishing sheets can be driven at different speeds toadjust the relative polishing rates at different portions of thesubstrate. The center and outer polishing sheets can be driven inopposite directions, or all the polishing sheets can be driven in thesame direction, or the two outer polishing sheets can be driven inopposite directions (one of which will match the direction of the centerpolishing sheet).

The invention is not limited to the embodiments depicted and described.Rather, the scope of the invention is defined by the appended claims.

1. A chemical mechanical polishing apparatus, comprising: a firstpolishing station including a movable platen, a generally linearpolishing sheet, and a drive mechanism supporting the polishing sheetwith a portion of the polishing sheet extending over the platen, thedrive mechanism configured to incrementally advance the polishing sheetin a linear direction relative to the platen; and a second polishingstation including a rotatable platen, a polishing pad composed of anapped poromeric material attached to the rotatable platen; and aconditioner having a conditioner head to condition the polishing pad. 2.The apparatus of claim 1, wherein the conditioner includes an arm, andthe conditioner head is suspended on the end of the arm.
 3. Theapparatus of claim 2, wherein the conditioner includes a supportassembly to rotate the arm so as sweep the conditioner head over thepolishing pad.
 4. The apparatus of claim 1, wherein the conditioner headincludes a conditioning disk having a side impregnated with diamonds forscraping the polishing pad.
 5. The apparatus of claim 1, wherein thepolishing pad is embossed or stamped with a pattern.
 6. The apparatus ofclaim 1, wherein the polishing pad is attached to the rotatable platenby a pressure-sensitive adhesive layer.
 7. The apparatus of claim 1,wherein the polishing pad consists of a single layer.
 8. A method ofpolishing a substrate, comprising: polishing a substrate with agenerally linear polishing sheet; polishing the substrate with polishingpad composed of a napped poromeric material; and conditioning thepolishing pad.
 9. The method of claim 8, wherein conditioning thepolishing pad includes scraping the napped poromeric material withdiamonds.
 10. The method of claim 9, wherein conditioning the polishingpad includes sweeping the conditioner head over the polishing pad. 11.The method of claim 8, wherein polishing the substrate with thepolishing pad includes rotating the polishing pad.
 12. The method ofclaim 8, wherein polishing the substrate with the polishing pad occursafter polishing the substrate with the polishing sheet.
 13. The methodof claim 8, wherein polishing the substrate with the polishing padincludes distributing slurry with a pattern embossed or stamped on thepolishing pad.
 14. The method of claim 8, wherein the polishing padconsists of a single layer.
 15. An assembly for a chemical mechanicalpolisher, comprising: a roller; a first generally linear polishing sheetwound around the roller; a second generally linear polishing sheet woundaround the roller and spaced apart from the first polishing sheet. 16.The assembly of claim 15, wherein the first polishing sheet and thesecond polishing sheet are formed of the same polishing material. 17.The assembly of claim 15, wherein the first polishing sheet and thesecond polishing sheet are formed of different polishing materials.